Known in the art is an air purifying apparatus (cf., an advertising publication D.6 by the English firm of Spencer and Halstead Ltd., p.2) wherein contaminated air is drawn off by a fan and directed to the inner spaces of hose filters to be purified from impurities by passing through the walls of said filters. The cleaning of the filters of the impurities deposited on their inner surfaces is done manually, to which end the filters are to be unfastened and removed from the apparatus.
There is also known an air purifying apparatus (cf., an advertising publication by the Dutch branch of Torit (U.S.A.), Publication GBF-72F, p.3 a figure on the right) wherein the filtering material is stretched over rectangular frames. The filters are cleaned manually after being unfastened and removed from the apparatus.
Another prior art apparatus for purifying air (cf., a model "Kleinstfilter" (Normalausfuhrung) by Ventilatorenfabrik Oelde GmbH, BRD) has filters attached to the inner side of an opening cover. The filters are cleaned manually by means of a brush with the cover opened.
One more prior art air purifying apparatus (cf., the advertising publication D.6 by the English firm of Spencer and Halstead Ltd, p. 3) has the filtering material stretched over triangular frames suspended from a rack with a handle extending outwards. The filters are cleaned manually by shaking them by means of the handle.
In still another prior art apparatus (cf., a model monobloc-Entstauber m 120 and m 150 by Wieland KG lufttechnik BRD) the ends of filters are shaped as round hoses and are fixed in two plates of which the top plate is movable. The cleaning of the filters is done by shaking the hoses by way of manually effected reciprocation of the top plate in the vertical direction by means of an outwardly extending handle.
Prior art apparatus for drawing off dust and fine shavings lack suppressors of noise caused by the air leaving the apparatus. This air featurin g substantial volume and high velocity causes considerable noise on being discharged directly to the atmosphere from the apparatus.
Closest of all to the disclosed apparatus is an apparatus for purifying air (cf., Yu. V. Abrosimov, Frame-Type Glass Cloth Filters Developed in NIIOGAZ, published in Russian by Mashinostroiyeniye Publishers, Moscow, 1972, pp. 64-65) in which a set of filter elements comprising frames covered with filtering material stretched thereon are mounted on a horizontally extending hollow perforated shaft resting at the edges against bearings secured on the body of a filtering chamber. One end of the hollow shaft is closed while the other end is connected to an air draft stimulator (fan). During the operation of the apparatus, the hollow shaft with the filter elements rotates continuously by the action of an independent electric motor.
The air supplied to the filtering chamber of the apparatus passes through the filtering material from the outside to the inner space of the filter elements and then via openings in the wall of the hollow shaft and further along the inner space of the shaft to the fan. Impurities contained in the gas supplied to the apparatus tend to deposit on the surface of the filter elements, however, due to the centrifugal force developd upon rapid rotation of said filter elements, the gas adjacent to the filter elements is repelled from the latter such that the impurities (with the exception of finer ones) are prevented from depositing on the surface of the filter elements. As a result of this, the filtering cloth is slightly clogged therefore only loses its filtering power to a very minor extent.
In order to preclude the deposition of impurities on the surface of the filter elements, the latter should be rotated at a high speed. In so doing, however, the layer of air adjacent to the filter elements is repelled from the latter with a considerable force which sets up a great obstacle to the passage through the filtering cloth of air under the effect of a section or rarefaction produced by the fan, which results in an extremely low efficiency of the apparatus.
The finest impurity particles deposited on the surface of the filtering material hold on in spite of the rotation of the filter elements, due to the "suction" adherence to their surface under the effect of high evacuation produced by the fan in the inner space of the filter elements.